Comparison of Inhaled Nitric Oxide Versus Oxygen on Hemodynamics in Patients With Mitral Stenosis and Severe Pulmonary Hypertension After Mitral Valve Surgery

Pulmonary hypertension represents an important cause of morbidity and mortality in patients with mitral stenosis who undergo cardiac surgery, especially in the postoperative period. The aim of this study was to test the hypothesis that inhaled nitric oxide (iNO) would improve the hemodynamic effects and short-term clinical outcomes of patients with mitral stenosis and severe pulmonary hypertension who undergo cardiac surgery in a randomized, controlled study. Twenty-nine patients (4 men, 25 women; mean age 46 2 years) were randomly allocated to receive iNO (n = 14) or oxygen (n = 15) for 48 hours immediately after surgery. Hemodynamic data, the use of vasoactive drugs, duration of stay, and short-term complications were assessed. No differences in baseline characteristics were observed between the groups. After 24 and 48 hours, patients receiving iNO had a significantly greater increase in cardiac index compared to patients receiving oxygen (p < 0.0001). Pulmonary vascular resistance was also more significantly reduced in patients receiving iNO versus oxygen (-117 dyne/s/cm(5), 95% confidence interval 34 to 200, vs 40 dyne/s/cm5, 95% confidence interval 34 to 100, p = 0.005) at 48 hours. Patients in the iNO group used fewer systemic vasoactive drugs.(mean 2.1 +/- 0.14 vs 2.6 +/- 0.16, p = 0.046) and had a shorter intensive care unit stay (median 2 days, interquartile range 0.25, vs median 3 days, interquartile range 7, p = 0.02). In conclusion, iNO immediately after surgery in patients with mitral stenosis and severe pulmonary hypertension improves hemodynamics and may have short-term clinical benefits. (C) 2011 Elsevier Inc. All rights reserved. (Am J Cardiol 2011;107:1040-1045)

Exhaled nitric oxide as a predictor of exacerbation in children with moderate-to-severe asthma: a prospective, 5-month study

Background: Inhaled corticosteroids (ICSs) are recommended as the first line of treatment in children with moderate-to-severe asthma. Exhaled nitric oxide (ENO) has been proposed as a clinically useful marker of control that might help identify patients in whom ICS dose may be safely reduced. Objective: To evaluate the ability of ENO to predict future asthma exacerbations in children with moderate-to-severe asthma undergoing ICS tapering. Methods: This is an observational study with no control group. ENO was measured biweekly for 14 weeks in 32 children with moderate-to-severe asthma who were undergoing ICS tapering. Clinical evaluations and spirometry were performed concomitantly, and families kept daily diaries to record symptoms between visits. We used generalized estimating equations to model the In (odds) of an asthma exacerbation in the subsequent 2-week interval as a function of ENO level at the start of the interval while adjusting for age, sex, asthma severity, and current medication use. Results: We were able to successfully lower ICS doses in 10 (56%) of the 18 children with moderate asthma and in 3 (21%) of the 14 children with severe asthma. In 83 of the 187 follow-up clinical evaluations, children were determined to have had an exacerbation during the preceding 2 weeks. ENO levels, whether expressed as a continuous variable or dichotomized, were not associated with future risk for exacerbations in either unadjusted or adjusted models. Conclusion: ENO was not a useful clinical predictor of future asthma exacerbations for children with moderate-to-severe asthma undergoing ICS tapering. Ann Allergy Asthma Immunol. 2009; 103:206-211.

Exhaled nitric oxide for monitoring childhood asthma inflammation compared to sputum analysis, serum interleukins and pulmonary function

The level of fractional exhaled nitric oxide (FENO) is significantly elevated in uncontrolled asthma and decreases after anti-inflammatory therapy The aim of this prospective study was to analyze the behavior of FENO in the follow-up and management of the inflammation in asthmatic pediatric patients treated with inhaled corticosteroids (ICS), compared to sputum cellularity, serum interleukins (IL), and pulmonary function. Twenty-six clinically stable asthmatic children aged from 6 to 18 years, previously treated or not with ICS were included. Following an international consensus (GINA), the patients were submitted to standard treatment with inhaled fluticasone for 3 months according to the severity of the disease. During this period, each patient underwent three assessments at intervals of approximately 6 weeks: Each evaluation consisted of the measurement of FENO, determination of serum interleukins IL-5, IL-10, IL-13, and interferon gamma (INF-gamma), spirometry and cytological analysis of spontaneous or induced sputum. A significant reduction in mean FENO and IL-5, without concomitant changes in FEV1, was observed along the study. There was no significant correlation between FeNO and FEV1 in the three assessments. A significant correlation between FeNO and IL-5 levels was only observed in the third assessment (r = 0.499, P=0.025). In most patients, serum IL-10, IL-13, and INF-gamma concentrations were undetectable throughout the study Sputum samples were obtained spontaneously in 11 occasions and in 56 by induction with 3% hypertonic saline solution (success rate: 50.8%), with 39 (69.9%) of them adequate for analysis. Only two of the 26 patients produced adequate samples in the three consecutive evaluations, which impaired the determination of a potential association between sputum cellularity and FeNO levels throughout the study. In conclusion, among the parameters of this study, it was difficult to perform and to interpret the serial analysis of spontaneous or induced sputum. Serum interleukins, which remained at very low or undetectable levels in most patients, were not found to be useful for therapeutic monitoring, except for IL-5 that seems to present some correlation with levels of FeNO exhaled. Monitoring of the mean FEV1 indicated no significant variations during the treatment, demonstrating that functional stability or the absence of obstruction may not reflect the adequate management of asthma. Serial measurement of FeNO seemed to best reflect the progressive anti-inflammatory action of ICS in asthma.

Nitric oxide modulates lipopolysaccharide-induced endothelial platelet endothelial cell adhesion molecule expression via interleukin-10

We have shown previously that nitric oxide (NO) controls platelet endothelial cell adhesion molecule (PECAM-1) expression on both neutrophils and endothelial cells under physiological conditions. Here, the molecular mechanism by which NO regulates lipopolysaccharide (LPS)-induced endothelial PECAM-1 expression and the role of interleukin (IL)-10 on this control was investigated. For this purpose, N-(G)-nitro-L-arginine methyl ester (L-NAME; 20 mg/kg/day for 14 days dissolved in drinking water) was used to inhibit both constitutive (cNOS) and inducible nitric oxide (iNOS) synthase activities in LPS-stimulated Wistar rats (5 mg/kg, intraperitoneally). This treatment resulted in reduced levels of serum NO. Under this condition, circulating levels of IL-10 was enhanced, secreted mainly by circulating lymphocytes, dependent on transcriptional activation, and endothelial PECAM-1 expression was reduced independently on reduced gene synthesis. The connection between NO, IL-10 and PECAM-1 expression was examined by incubating LPS-stimulated (1 mu g/ml) cultured endothelial cells obtained from naive rats with supernatant of LPS-stimulated lymphocytes, which were obtained from blood of control or L-NAME-treated rats. Supernatant of LPS-stimulated lymphocytes obtained from L-NAME-treated rats, which contained higher levels of IL-10, reduced LPS-induced PECAM-1 expression by endothelial cells, and this reduction was reversed by adding the anti-IL-10 monoclonal antibody. Therefore, an association between NO, IL-10 and PECAM-1 was found and may represent a novel mechanism by which NO controls endothelial cell functions.

Role of nitric oxide in hyperpnea-induced bronchoconstriction and airway microvascular permeability in guinea pigs

The present study aimed to evaluate the role of nitric oxide (NO) on hyperpnea-induced bronchoconstriction (HIB) and airway microvascular hyperpermeability (AMP). Sixty-four guinea pigs were anesthetized, tracheotonnized, cannulated, and connected to animal ventilator to obtain pulmonary baseline respiratory system resistance (Rrs). Animals were then submitted to 5 minutes hyperpnea and Rrs was evaluated during 15 minutes after hyperpnea. AMP was evaluated by Evans blue dye (25 mg/kg) extravasation in airway tissues. Constitutive and inductible NO was evaluated by pretreating animals with N(G)-nitro-1-arginine methyl ester (I-NAME) (50 mg/kg), aminoguadinine (AG) (50 mg/kg), and I-arginine (100 mg/kg) and exhaled NO (NOex) was evaluated before and after drug administration and hyperpnea. The results show that I-NAME potentiated (57%) HIB and this effect was totally reversed by I-arginine pretreatment, whereas AG did not have effect on HIB. I-NAME decreased basal AMP (48%), but neither I-NAME nor AG had any effect on hyperpnea-induced AMP. NOex levels were decreased by 50% with I-NAME, effect that was reversed by I-arginine treatment. These results suggest that constitutive but not inducible NO could have a bronchoprotective effect on HIB in guinea pigs. The authors also observed that neither constitutive nor inducible NO seems to have any effect on hyperpnea-induced AMP.

Erection induced by Tx2-6 toxin of Phoneutria nigriventer spider: Expression profile of genes in the nitric oxide pathway of penile tissue of mice

The peptides Tx2-5 and Tx2-6, isolated from the whole venom of ""armed-spider"" Phoneutria nigniventer venom, are directly linked with the induction of persistent and painful erection in the penis of mammals. The erection induced by Tx2-6 has been associated with the activation of nitric oxide synthases. There is a scarcity of studies focusing on the outcome of Tx2-6 at the molecular level, by this reason we evaluated the gene profile activity of this toxin at the nitric oxide (NO) pathway. After microarray analyses on cavernous tissue of mice inoculated with Tx2-6 we found that only 10.4% (10/96) of these genes were differentially expressed, showing a limited effect of the toxin on the NO pathway. We found the genes sparc, ednrb, junb, cdkn1a, bcl2, ccl5, abcc1 over-expressed and the genes sod1, s100a10 and fth1 under-expressed after inoculation of Tx2-6. The differential expressions of sparc and ednrb genes were further confirmed using real-time PCR. Interestingly, ednrb activates the L-arginine/NO/cGMP pathway that is involved in the relaxation of the cavernous body. Therefore the priapism induced by Tx2-6 is a consequence of a highly specific interference of this neurotoxin with the NO pathway. (C) 2009 Elsevier Ltd. All rights reserved.

The expression of contextual fear conditioning involves activation of an NMDA receptor-nitric oxide pathway in the medial prefrontal cortex

The ventral portion of medial prefrontal cortex (vMPFC) is involved in contextual fear-conditioning expression in rats. In the present study, we investigated the role of local N-methyl-D-aspartic acid (NMDA) glutamate receptors and nitric oxide (NO) in vMPFC on the behavioral (freezing) and cardiovascular (increase of arterial pressure and heart rate) responses of rats exposed to a context fear conditioning. The results showed that both freezing and cardiovascular responses to contextual fear conditioning were reduced by bilateral administration of NMDA receptor antagonist LY235959 (4 nmol/200 nL) into the vMPFC before reexposition to conditioned chamber. Bilateral inhibition of neuronal NO synthase (nNOS) by local vMPFC administration of the N omega-propyl-L-arginine (N-propyl, 0.04 nmol/200 nL) or the NO scavenger carboxy-PTI0 (1 nmol/200 A) caused similar results, inhibiting the fear responses. We also investigated the effects of inhibiting glutamate- and NO-mediated neurotransmission in the vMPFC at the time of aversive context exposure on reexposure to the same context. It was observed that the 1st exposure results in a significant attenuation of the fear responses on reexposure in vehicle-treated animals, which was not modified by the drugs. The present results suggest that a vMPFC NMDA-NO pathway may play an important role on expression of contextual fear conditioning.

Local profile of cytokines and nitric oxide in patients with bacterial vaginosis and cervical intraepithelial neoplasia

Objective: To evaluate the local immune response in patients with bacterial vaginosis (BV) and cervical intraepithelial neoplasia (CIN), as assessed by cytokine and nitric oxide (NO) concentrations. Study design: Patients attending for routine gynaecological examination were prospectively enrolled in groups: BV (n = 25) diagnosed by clinical criteria, CIN graded I to III (n = 35, 6 CIN 1, 8 CIN 11 and 21 CIN 111) by histological analysis, and controls (n = 15) without clinical and cytological findings. Randomly selected patients within CIN group at grades 11 or III (n = 15) were re-evaluated at 60 days after surgical treatment. Endocervical (EC) and vaginal secretion samples were collected by cytobrush and the levels of cytokines (ELISA) and NO metabolite (Griess reaction) were assayed. Results: NO was assessed in all subjects, and cytokines in all controls, 15 BV and 30 CIN patients. Interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10) and nitrite levels were higher in EC than in vaginal secretions in BV and CIN groups. In CIN group, IL-8, IL-10 and nitrite concentrations were greater in EC and/or vaginal secretions than in BV or controls. Surgical treatment reduced IL-8 levels in EC and vaginal secretions. Conclusion: A similar local immune profile was found in BV and CIN groups. The increased local production of IL-8, IL-10 and NO in CIN suggests a role for these mediators in the immune response against tumour or tumour development. (c) 2007 Elsevier Ireland Ltd. All rights reserved.

Peroxisome proliferator-activated receptor-gamma ligand, 15-deoxy-Delta A(12,14)-prostaglandin J(2), reduces neutrophil migration via a nitric oxide pathway

Ligands for peroxisome proliferator-activated receptor gamma (PPAR-gamma), such as 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) have been implicated as a new class of anti-inflammatory compounds with possible clinical applications. Based on this concept, this investigation was designed to determine the effect of 15d-PGJ(2)-mediated activation of PPAR-gamma ligand on neutrophil migration after an inflammatory stimulus and clarify the underlying molecular mechanisms using a mouse model of peritonitis. Our results demonstrated that 15d-PGJ(2) administration decreases leukocyte rolling and adhesion to the inflammated mesenteric tissues by a mechanism dependent on NO. Specifically, pharmacological inhibitors of NO synthase remarkably abrogated the 15d-PGJ(2)-mediated suppression of neutrophil migration to the inflammatory site. Moreover, inducible NOS(-/-) mice were not susceptible to 15d-PGJ(2)-mediated suppression of neutrophil migration to the inflammatory sites when compared with their wild type. In addition, 15d-PGJ(2)-mediated suppression of neutrophil migration appeared to be independent of the production of cytokines and chemokines, since their production were not significantly affected in the carrageenan-injected peritoneal cavities. Finally, up-regulation of carrageenan-triggered ICAM-I expression in the mesenteric microcirculation vessels was abrogated by pretreatment of wild-type mice with 15d-PGJ(2), whereas 15d-PGJ(2) inhibited F-actin rearrangement process in neutrophils. Taken together these findings demonstrated that 15d-PGJ(2) suppresses inflammation-initiated neutrophil migration in a mechanism dependent on NO production in mesenteric tissues.

Antihypertensive effects exerted by enalapril in mild to moderate hypertension are not associated with changes in the circulating levels of nitric oxide-related markers

The antihypertensive effects of angiotensin-converting enzyme inhibitors (ACEi) are explained, at least in part, by enhanced bradykinin-dependent nitric oxide (NO) formation and decreased angiotensin II-induced oxidative stress and vasoconstriction. We examined for the first time whether treatment with enalapril increases the plasma levels of markers of NO formation and decreases oxidative stress in mild to moderate hypertensive patients. Eighteen untreated hypertensive patients were treated with enalapril 10 mg/day (n = 10) or 20 mg/day (n = 8) for 60 days. Eighteen normotensive healthy controls were followed for the same period. Venous blood samples were collected at baseline and after 30/60 days of treatment with enalapril. Plasma NOx (nitrites + nitrates) concentrations were determined by using the Griess reaction. Plasma nitrite and whole blood nitrite concentrations were determined by using an ozone-based chemiluminescence assay. Plasma thiobarbituric acid-reactive species (TBARS) and 8-isoprostane concentrations were determined by a fluorimetric method and by ELISA, respectively. Treatment with enalapril decreased blood pressure in hypertensive patients. However, we found no significant changes in plasma NOx, nitrite, whole blood nitrite, and in the levels of markers of oxidative stress in both normotensive controls and hypertensive patients treated with enalapril. Our data show that enalapril 10-20 mg/day does not affect the concentrations of relevant markers of NO formation or markers of oxidative stress in mild to moderately hypertensive subjects, despite satisfactory blood pressure control. Our findings do not rule out the possibility that ACEi may produce such effects in more severely hypertensive patients treated with higher doses of ACEi.

eNOS haplotype associated with hypertension in obese children and adolescents

Objective: The aim of our study is to investigate whether genetic polymorphisms in the endothelial nitric oxide synthase (eNOS) gene (in the promoter region T(-786)C, in exon 7 (Glu298Asp) and in intron 4 (4b/4a)) or eNOS haplotypes are associated with hypertension in obese children and adolescents. Methods: We genotyped 175 healthy (controls), 110 normotensive obese and 73 hypertensive obese children and adolescents. Genotypes were determined by Taqman allele discrimination assay and real-time PCR, and by PCR followed by fragment separation by electrophoresis. We compared the distribution of eNOS genotypes, alleles and haplotypes in the three study groups of subjects. We have also measured whole-blood nitrite concentrations. Results: The 4a4a genotype for the intron 4 polymorphism was more common in normotensive obese and hypertensive obese (P < 0.01). The AspAsp genotype for Glu298Asp polymorphism was less common in normotensive obese (P < 0.02). No significant differences were found in allele distributions for the three eNOS polymorphisms. However, the haplotype combining the C, 4b and Glu variants for the three polymorphisms was more common in hypertensive obese than in normotensive obese or control children and adolescents (odds ratio = 2.28 and 2.79, respectively; 95% confidence interval: 1.31-4.31 and 1.39-5.64, respectively; both P < 0.00625). This haplotype was not associated with significantly different nitrite concentrations (P > 0.05). Conclusions: Our findings suggest that the eNOS haplotype, C b Glu, is associated with hypertension in obese children and adolescents. Further studies examining the possible interactions of eNOS haplotypes with environmental factors and other genetic markers involved in the development of obesity and its complications are warranted. International Journal of Obesity (2011) 35, 387-392; doi:10.1038/ijo.2010.146; published online 27 July 2010

Nitric Oxide-Induced Vasorelaxation in Response to PnTx2-6 Toxin from Phoneutria nigriventer Spider in Rat Cavernosal Tissue

Introduction. Priapism is one of several symptoms observed in accidental bites by the spider Phoneutria nigriventer. The venom of this spider is comprised of many toxins, and the majority has been shown to affect excitable ion channels, mainly sodium (Na+) channels. It has been demonstrated that PnTx2-6, a peptide extracted from the venom of P. nigriventer, causes erection in anesthetized rats and mice. Aim. We investigated the mechanism by which PnTx2-6 evokes relaxation in rat corpus cavernosum. Main Outcome Measures. PnTx2-6 toxin potentiates nitric oxide (NO)-dependent cavernosal relaxation. Methods. Rat cavernosal strips were incubated with bretylium (3 x 10-5 M) and contracted with phenylephrine (PE; 10-5 M). Relaxation responses were evoked by electrical field stimulation (EFS) or sodium nitroprusside (SNP) before and after 4 minutes of incubation with PnTx2-6 (10-8 M). The effect of PnTx2-6 on relaxation induced by EFS was also tested in the presence of atropine (10-6 M), a muscarinic receptor antagonist, N-type Ca2+ channel blockers (omega-conotoxin GVIA, 10-6 M) and sildenafil (3 x 10-8 M). Technetium99m radiolabeled PnTx2-6 subcutaneous injection was administrated in the penis. Results. Whereas relaxation induced by SNP was not affected by PnTx2-6, EFS-induced relaxation was significantly potentiated by this toxin as well as PnTx2-6 plus SNP. This potentiating effect was further increased by sildenafil, not altered by atropine, however was completely blocked by the N-type Ca2+ channels. High concentrated levels of radiolabeled PnTx2-6 was specifically found in the cavernosum tissue, suggesting PnTx2-6 is an important toxin responsible for P. nigriventer spider accident-induced priapism. Conclusion. We show that PnTx2-6 slows Na+ channels inactivation in nitrergic neurons, allowing Ca2+ influx to facilitate NO/cGMP signalling, which promotes increased NO production. In addition, this relaxation effect is independent of phosphodiesterase enzyme type 5 inhibition. Our data displays PnTx2-6 as possible pharmacological tool to study alternative treatments for erectile dysfunction. Nunes KP, Cordeiro MN, Richardson M, Borges MN, Diniz SOF, Cardoso VN, Tostes R, De Lima ME, Webb RC, and Leite R. Nitric oxide-induced vasorelaxation in response to PnTx2-6 toxin from Phoneutria nigriventer spider in rat cavernosal tissue. J Sex Med 2010;7:3879-3888.

NOC-9, a selective nitric oxide donor, induces flight reactions in the dorsolateral periaqueductal gray of rats by activating soluble guanylate cyclase

Previous studies have showed that SIN-1, a nitric oxide (NO) donor, injected into the dorsolateral column of the periaqueductal gray (dlPAG) induces flight reactions. This drug, however, can also produce peroxynitrite, which may interfere in this effect. In addition, it is also unknown if this effect is mediated by local activation of soluble guanylate cyclase (sGC). The aims of this study, therefore, were (1) to investigate if NOC-9 (6-(2-Hydroxy-1-methyl-2-nitrosohydrazino)-N-methyl-1-hexanamine), a NO donor that does not produce peroxynitrite, would produce flight reactions after intra-dlPAG administration similar to those induced by SIN-1; (2) to verify if these responses could be prevented by local injection of a selective guanylate cyclase inhibitor (ODQ). Male Wistar rats (n = 5-12) with cannulae aimed at the dlPAG received injections of TRIS (pH 10.0, 0.5 mu l), NOC-9 (75 and 150 nmol), saline or SIN-1 (200 nmol) and were placed in an open arena for 10 min. In a subsequent experiment animals (n = 7-8) were pretreated with ODQ (1 nmol/0.5 mu l) before receiving NOC-9 150 nmol. NOC-9 induced a significant dose-dependent increase in flight reactions in the first minute after injection (% of animals displaying flight: vehicle = 0%, NOC 75 = 67%. NOC 150 = 75%). SIN-1 had a similar effect (100% of animals showing flight) but the effects lasted longer (10 min) than those of NOC-9. The effect of NOC-9 (150 nmol) was prevented by pretreatment with ODQ (% of animals displaying flight: vehicle + NOC 150 = 71 %, ODQ + NOC 150 = 37%). The results suggest that NO donors injected into the dlPAG induce defensive responses that are not mediated by secondary peroxynitrite production. Moreover, they also indicate that these defensive responses depend on activation of local sGC. The data strengthen the proposal that NO can modulate defensive reactions in the dlPAG. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

GABA and nitric oxide in the PVN are involved in arterial pressure control but not in the chemoreflex responses in rats

GABAergic, nitrergic and glutamatergic mechanisms in the PVN on the baseline mean arterial pressure (MAP), heart rate (HR) and on the cardiovascular responses to chemoreflex activation in awake rat were evaluated. Chemoreflex was activated with KCN before and after microinjections into the PVN. Bicuculline into the PVN increased baseline MAP (94+/-3 vs 113+/-5 mmHg) and HR (350+/-9 vs 439+/-18 bpm) but had no effect on the pressor (49+/-5 vs 47+/-6 mmHg) or bradicardic (-213+/-23 vs -256+/-42 bpm) responses (n=7). Kynurenic acid into the PVN (n=6) produced no significant changes in the MAP (98+/-3 vs 100+/-3 mmHg), HR (330+/-5 vs 339+/-12 mmHg) or in the pressor (50+/-4 vs 42+/-4 mmHg) and bradicardic (-252+/-4 vs -285+/-16 bpm) responses to chemoreflex. L-NAME into the PVN (n=8) produced increase in the MAP (94+/-3 vs 113+/-5 mmHg) and HR (350+/-9 vs 439+/-18 bpm) but had no effect on the pressor (52+/-5 vs 47+/-6 mmHg) or bradicardic (-253+/-19 vs -320+/-25 bpm) responses to chemoreflex. We conclude that GABA(A) and nitric oxide in the PVN are involved in the maintenance of the baseline MAP but not in the modulation of the responses to chemoreflex. The results also show that Glutamate receptors in the PVN are not involved in maintenance of the baseline MAP, HR or in the cardiovascular responses to chemoreflex in awake rats. (C) 2008 Elsevier B.V. All rights reserved.

Nitric oxide modulates the firing rate of the rat supraoptic magnocellular neurons

In vitro, nitric oxide (NO) inhibits the firing rate of magnocellular neurosecretory cells (MNCs) of hypothalamic supraoptic and paraventricular nuclei and this effect has been attributed to GABAergic activation. However, little is known about the direct effects of NO in MNCs. We used the patch-clamp technique to verify the effect Of L-arginine, a precursor for NO synthesis, and N-omega-nitro-L-arginine methyl ester hydrochloride (L-NAME), an inhibitor of NOS, on spontaneous electrical activity of MNCs after glutamatergic and GABAergic blockade in Wistar rat brain slices. 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 mu M) and DL-2-amino-5-phosphonovaleric acid (DL-AP5) (30 mu M) were used to block postsynaptic glutamatergic currents, and picrotoxin (30 mu M) and saclofen (30 mu M) to block ionotropic and metabotropic postsynaptic GABAergic currents. Under these conditions, 500 mu M L-arginine decreased the firing rate from 3.7 +/- 0.6 Hz to 1.3 +/- 0.3 Hz. Conversely, 100 mu M L-NAME increased the firing rate from 3.0 +/- 0.3 Hz to 5.8 +/- 0.4 Hz. All points histogram analysis showed changes in resting potential from -58.1 +/- 0.8 mV to -62.2 +/- 1.1 mV in the presence of L-arginine and from -59.8 +/- 0.7 mV to -56.9 +/- 0.8 mV by L-NAME. Despite the nitrergic modulator effect on firing rate, some MNCs had no significant changes in their resting potential. In those neurons, hyperpolarizing after-potential (HAP) amplitude increased from 12.4 +/- 1.2 mV to 16.8 +/- 0.7 mV by L-arginine, but without significant changes by L-NAME treatment. To our knowledge, this is the first demonstration that NO can inhibit MNCs independent of GABAergic inputs. Further, our results point to HAP as a potential site for nitrergic modulation. (C) 2008 IBRO. Published by Elsevier Ltd. All rights reserved.